The polymerization of olefins with the use of Ziegler-Natta catalysts is an established technique known since the early 1950s and is widely applied in industry. Ziegler-Natta catalysts are based on transition metal compounds, especially titanium and organoaluminium compounds. Numerous metal complexes have been described in the literature as catalysts for olefin polymerization, among the publications are literature references teaching amidinate and guanidinate metal complexes and their use as polymerization catalysts such as WO 97/45434, U.S. Pat. Nos. 5,777,120 and 5,502,128. Bis(trimethylsilyl)benzamidinate zirconium dichlorides are taught by D. Herskovics-Korine in JOURNAL OF ORGANOMETALLIC CHEMISTRY, vol. 503, no. 2, 15 Nov. 1995, pages 307-314 as active catalysts in presence of a co-catalyst (methylaluminoxane, MAO) for polyethylene (PE) production. The use of Titanium monoamidinate-MAO catalysts for the polymerization of propene, styrene, and 1,3-butadiene is taught by Liguori et al. in MACRO-MOLECULES, vol. 36, no. 15, 1 Jul. 2003, pages 5451-5458. M. Zhou et al. in JOURNAL OF ORGANOMETALLIC CHEMISTRY, vol. 692, no. 23, 6 Oct. 2007, pages 5195-5202 teach the use of tris guanidinato zirconium and hafnium complexes as catalysts for PE production in presence of a co-catalyst MAO or Et2AlCl. A further publication of M. Zhou et al. in INORGANIC CHEMISTRY COMMUNICATIONS, vol. 10, no. 11, 18 Oct. 2007, pages 1262-1264 relates to the synthesis and structure of non-symmetric zirconium guanidinato dimer complexes and their use in PE production in combination with MAO, MMAO (modified MAO) and Et2AlCl. A review by S. Collins of different amidinate and guanidate catalysts and their use as polymerization catalysts is published in COORDINATION CHEMISTRY REVIEWS, vol. 255, no. 1-2, 1 Jan. 2011, pages 118-138. None of the above references is concerned with CCTP yielding oligomers of relatively low molecular weight and allowing the production of long chain alcohols or alpha olefins. Moreover, none of the catalyst systems is capable of producing Al-terminated oligomers.
A great variety of catalysts capable of catalyzing coordinative chain transfer polymerization (CCTP) has been proposed in the literature. CCTP is commonly used to control and modify molecular weights of polymers. These transition metal based catalysts are typically used together with co-catalysts which usually act as chain transfer agents. Suitable co-catalysts include alkyl zinc, alkyl aluminium, alkyl aluminium halides and alkyl alumoxanes, commonly used together with inert, non-coordinating ion forming compounds (activator), Lewis and Brönstedt acids and mixtures thereof. Such prior art processes are disclosed in W. P. Kretschmer et al.; Chem. Eur. J. 2006, 12, 8969-8978 and S. B. Amin, T. J. Marks; Angew. Chem. 2008, 120, 2034-2054 and Zinck et al.; Chem. Rev. 2013; DOI: dx.doi.org/10.1021/cr300289z.
One characteristics of CCTP is that polymer chains are end-capped with the respective main group metal of the co-catalyst and can be further functionalized (M. Bialek, J. Polym. Sci.: Part A: Polym. Chem. 2010, 48, 3209-3214 and W. P. et al., Dalton Trans. 2010, 39, 6847-6852).
CCTP typically requires the use of a metal complex as catalyst, a co-catalyst and optionally an activator. In the understanding of the present invention the co-catalyst is a chain transfer agent and may optionally but not necessarily be an activator at the same time. The activator may be for example a compound different from the chain transfer agent and not functioning as a chain transfer agent. Such activator in the understanding of the invention is under above circumstances not called a co-catalyst and only an activator.
Catalyst systems used in CCTP are often prone to ligand transfer from the catalyst onto the co-catalyst which results in a decreased activity (W. P. Kretschmer, B. Hessen, A. Noor, N. M. Scott, R. J. Kempe, Organomet. Chem. 2007, 692, 4569-4579). Especially, at high co-catalyst to catalyst ratios the catalyst activity is remarkably decreased. Hence, all known catalyst systems suffer from un-wanted olefin production due to β-hydride elimination. It is therefore an objective of the present invention to provide highly active catalysts showing only minor β-hydrid elimination and accordingly less side products (I. Haas, W. P. Kretschmer, R. Kempe, Organometalics 2011, 30, 4854-4861). Besides the total chain transfer efficiency should be close to 100%. In addition the catalyst should be capable of operating at high co-catalyst to catalyst ratios thereby suppressing β-hydrid elimination in view of the fact that the co-catalyst acts as chain transfer agent.
EP 0329891 A2 for instance discloses certain low molecular weight polyethylene alcohols having an average chain length of from about 20 to about 500 carbon atoms and a polydispersity of 1.04 to 1.20 and their conversion to end-functionalized polymers by introducing a functional group which replaces the hydroxyl group of the alcohol. The following functional groups are taught: halogen, alkanolamine, carboxyl, thiol, amine, quaternized amine radical, amide, quaternized dialkylamine, amine oxide, silyl and others.
The object of the present invention is to find stable highly active and selective metal complexes which are capable of polymerizing or co-polymerizing olefins and to finally transfer the produced carbon chain onto a co-catalyst. The co-catalyst thereby acts as a chain transfer agent and is functionalized with the carbon chain after the transfer. Subsequent to the transfer the obtained molecules can be derivatized via oxidation and hydrolyzation to yield functionalized carbon chains, in particular hydroxy terminated carbon chains. A further objective of the present invention is to provide a catalyst which can be prepared in an easy and economical fashion.